Avalanche Advisory

ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.

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The Bottom Line

After an intense period of heavy snowfall added 12-18" of new snow overnight, we have a HIGH avalanche danger above treeline this morning and a CONSIDERABLE avalanche danger at treeline. A MODERATE danger exists below 1,000' where avalanches occurring from above may run. The new snow fell in conjunction with strong Easterly winds and was deposited on a very weak pre-existing surface. Natural avalanches 1-3' thick have likely been occurring through the night and may persist today. HUMAN TRIGGERED AVALANCHES 1-3' thick WILL BE LIKELY today on slopes steeper than 30 degrees.

**Travel in avalanche terrain is not recommended until the snowpack has had time to adjust. Choose mellow terrain and avoid all runnout zones. If skies partially clear, the Alpine avalanche danger will trend to CONSIDERABLE, yet patience is still warranted due to a slow to stabilize snowpack.

Show the Complete North American Avalanche Danger Scale

North American Public Avalanche Danger Scale

Avalanche danger is determined by the likelihood, size and distribution of avalanches.

Danger Level

Travel Advice

Likelihood of Avalanches

Avalanche Size and Distribution

5 Extreme

Avoid all avalanche terrain.

Natural and human- triggered avalanches certain.

Large to very large avalanches in many areas.

4 High

Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

Natural avalanches likely; human- triggered avalanches very likely.

Large avalanches in many areas; or very large avalanches in specific areas.

Today will be a tricky day in the backcountry: It's Saturday after Christmas, many folks may be itching to get out and snowmachine, ski, snowboard, etc., we just had 12-18" of new snow and.... skies may clear up. The problem is, and the tricky part, will be keeping our terrain choices in check since HUMAN TRIGGERED AVALANCHES ARE LIKELY. Not only are we just hours away from a 'rapid loading' event, but all this new snow fell, with wind loading, onto a weak surface. Hence, bonding between the new and old snow is not expected to be quick. Reports from yesterday, just as the storm was ramping up, were that avalanche conditions were rapidly increasing and shooting cracks were seen at treeline.

Storm snow totals (10am yesterday to 6am this morning - rain fell before 800'):Turnagain Pass: 15" snow at 1,880' and likely 16-18" at 2,500' (higher amounts on North end of Pass and lesser amounts on the South end)Girdwood Valley: ~ 12" snow at 1,700', likely more at the higher elevationsSummit Lake: Only 1" of new snow...

Avalanche problems expected today:

WIND SLABS: With strong Easterly wind overnight and moderate Easterly winds remaining through today, we can expect windloaded slopes to be prime to avalanche. Triggering a wind slab 1-3' thick is likely and these may be triggered remotely from the ridgeline.

STORM SLABS: Temperatures increased between 10-15 degrees F during snowfall. This is a perfect set up for an "upside-down" storm; depositing denser snow on top of less dense snow, creating a slab avalanche problem in areas sheltered from the wind.

LOOSE SNOW AVALANCHES: Sluffs due to heavy snowfall likely occurred last night and again will be likely today. These have the ability to trigger a slab avalanche on their way down.

What this means is very conservative choices are necessary for a safe day, and a safe Christmas weekend, in the backcountry. Choosing to ride your snowmachine in the flats and skiing/snowboarding on slopes 30 degrees or less is recommended. If skies do clear today, or tomorrow for that matter, very careful snowpack assessment is needed before venturing into the steeper and avalanche prone terrain.

Avalanche Problem 2

Cornices are expected to have grown and be teetering on the brink of breaking today. Some of these likely broke off during the night, which in turn is one of the main triggers of naturally occurring avalanches. These may break naturally today, triggering an avalanche below or easily triggered by people on a ridgeline.

Light snowfall began yesterday morning along with moderate winds from the East along the ridgetops. Late in the day, snowfall intensified, temperatures warmed ~10F and the Easterly winds began to cranked (averages in the 30 and 40'smph). Additionally, the rain snow line climbed from sea level to ~800' during the day. Snowfall totals at the mid-elevations are in the chart below.

Today, the brunt of the storm is through and we will have intermittent snow showers and partly cloudy skies throughout the region. In favored areas another 2-4" of snow is possible. The Easterly winds are expected to be 15-25mph on the ridgetops and temperatures in the low 20's F above treeline and near 30F at 1,000'.

Another intense Pacific storm is on track for Monday. Weather models are showing this system bringing the warmest air we have seen yet this season; along with intense precipitation and wind, we should see a rain/snow line between 1,000-2,000'.

PRECIPITATION 24-hour data (6am - 6am)

Temp Avg (F)

Snow (in)

Water (in)

Snow Depth (in)

Center Ridge (1880')

26

15

1.2

62

Summit Lake (1400')

28

1

0.1

17

Alyeska Mid (1700')

27

12

0.83

44

RIDGETOP 24-hour data (6am - 6am)

Temp Avg (F)

Wind Dir

Wind Avg (mph)

Wind Gust (mph)

Sunburst (3812')

19

NE

33

62

Seattle Ridge(2400')

22

SE

24

55

This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area (this advisory does not apply to highways, railroads, or operating ski areas).

Riding status is not associated with avalanche danger. An area will be open to motorized use in accordance to the Forest Management Plan when snow coverage is adequate to protect underlying vegetation. Backcountry hazards including avalanche hazard are always present regardless of the open status of motorized use areas.

(Updated: Dec 18, 2018 )

AREA

STATUS

WEATHER AND RIDING CONDITIONS

Glacier District

Johnson Pass:

Open

Please stay on trail to avoid resource damage through Forested areas.

Placer River:

Closed

Closed

Skookum Drainage:

Closed

Closed

Turnagain Pass:

Closed

Closed November 21 due to inadequate snow conditions. #hopeforsnow

Twentymile:

Closed

Closed

Seward District

Carter Lake:

Open

Lost Lake Trail:

Open

Please stay on trail to avoid resource damage through Forested areas.

Primrose Trail:

Open

Please stay on trail to avoid resource damage through Forested areas.

Resurrection Pass Trail:

Closed

Closed for the 2018/19 season. Next season will be open to motorized use.

The information in this advisory is from the U.S. Forest Service, which is solely responsible for its content. This advisory describes general avalanche conditions and local variations always occur.
This advisory provided by the Chugach National Forest, in partnership with Friends of the Chugach National Forest Avalanche Information Center.